CN102946807A

CN102946807A - X-ray CT device and control method for same

Info

Publication number: CN102946807A
Application number: CN2011800297012A
Authority: CN
Inventors: 冈部正和
Original assignee: Hitachi Medical Corp
Current assignee: Hitachi Ltd
Priority date: 2010-06-17
Filing date: 2011-06-16
Publication date: 2013-02-27
Anticipated expiration: 2031-06-16
Also published as: US20130094739A1; JPWO2011158893A1; JP5878119B2; US9025848B2; WO2011158893A1; CN102946807B

Abstract

Disclosed are an X-ray CT device and a control method for same, for generating X-ray CT images with optimum image quality for each portion and each region of an examinee, when scanning the examinee across a plurality of portions using a plane detector. The X-ray CT device is characterized by comprising: an X-ray source (11) which generates X rays; an X-ray detector (12); a rotation means (13) that rotates the X-ray source (11) and the X-ray detector (12), whilst maintaining the mutually facing arrangement of same; a smoothing means (230) and a filtering means (250) that generate a convolution filter based on the characteristics amount in projection data output from the X-ray detector (12) and superimpose the convolution filter on the projection data; a reconfiguration means (200) that makes reconfiguration calculations for the projection data on which the convolution filter is superimposed and generates an X-ray CT image of the examinee; and an image display means (280) that displays the image generated by the reconfiguration means (200).

Description

X ray CT device and control method thereof

Technical field

The present invention relates to X ray CT device, relate in particular to when crossing over the subject at a plurality of positions with the scanning of face detector, for each position of subject, X ray CT device and the control method thereof that each zone generates the X ray CT picture of best image quality.

Background technology

Generally, the output valve of X-ray detector, the scanning degree at the position that health thickness is large reduces, and error increases.Therefore, the zone that health thickness is larger, the noise of the X ray CT picture of reconstruct is larger.On the other hand, existing X ray CT device generates the X ray CT picture of subject usually with a reconfigurable filter for CT scan.Therefore, even can provide best X ray CT picture to certain position of subject, sometimes do not reach best image quality in other zones.

In this case, the known calculations a plurality of reconstructed images behind a plurality of reconfigurable filters such as smoothing wave filter, sharpening wave filter that superposeed, each reconstructed image is set additive operation coefficient and the addition corresponding with its CT value at each point, thus the X ray CT device of the X ray CT picture of the synthetic a plurality of reconstructed image gained of output.

The prior art document

Patent documentation

Patent documentation 1: TOHKEMY 2006-34785 communique

Summary of the invention

The problem that invention will solve

But above-mentioned X ray CT device calculates its reconstructed image in advance for a plurality of reconfigurable filters, therefore has the problem that needs operation time.In addition, particularly in the situation that use flat panel detector in the X-ray detector, because the noisiness of photographed data is large, therefore, if not the X-ray absorption coefficient of not only considering each reconstruction point (so-called CT value), the image quality (noise) of also considering reconstructed image determines whether using smoothing wave filter or sharpening wave filter, then has the problem that can't obtain good reconstruct CT picture.

In view of the above problems, the object of the present invention is to provide the increase that suppresses operation time, and generate the X ray CT device of the X ray CT picture of best image quality for each position.

Be used for solving the means of problem

The present invention realizes a kind of X ray CT device, and it generates based on the value of data for projection and the continually varying image processing filter, and carries out the image reconstruction computing, suppresses thus the increase of operation time, and generates the X ray CT picture of best image quality for each position.

In more detail, X ray CT device of the present invention is characterised in that to possess: the x-ray source that produces X ray; Configure relative with described x-ray source detected the described X ray that sees through subject, exports the X-ray detector of the data for projection of described subject; Make described x-ray source keep the rotary unit that rotates under the state of relative configuration with described X-ray detector; The wave filter generation unit of the image processing filter that the characteristic quantity of the pixel value that the generation basis comprises in described data for projection changes; For described data for projection, use the image processing filter of described generation to be reconstructed computing, generate the reconfiguration unit of the X ray CT picture of described subject; And the image-display units that shows described X ray CT picture.

The effect of invention

According to the present invention, a kind of X ray CT device can be provided, it suppresses the increase of operation time in the Cone-Beam CT photography of the subject of crossing over a plurality of positions with the scanning of face detector, for each position of subject, the X ray CT picture that each zone generates best image quality.

For example can realize a kind of X ray CT device, it is the Cone-Beam CT photography that crosses abdominal part from chest, can generate the X ray CT picture of high spatial resolution at the little chest region of X ray absorbtivity, the little abdomen area of output valve large in the X ray absorbtivity, X-ray detector can generate the outstanding X ray CT picture of low contrast resolution.

Description of drawings

Fig. 1-the 1st, the Sketch figure of cone-beam X-ray CT device of the present invention (C arm mode) 1 is used in expression.

Fig. 1-2 is illustrated in the Sketch figure that uses the C arm mode cone-beam X-ray CT device 1a that carries in the moving X-ray inspection apparatus of the present invention.

Fig. 2 is the block diagram of the structural element of expression filter transform information generating unit 220.

Fig. 3 is the block diagram of the structural element of expression smoothing unit 230.

Fig. 4 is the block diagram of the structural element of expression filter unit 250.

Fig. 5 is the schematic diagram that the expression convolution filter is set an example of picture 30.

Fig. 6 is the schematic diagram that the expression input filter is set an example of picture 40.

Fig. 7 is that expression is by the flow chart of the flow process of the reconstruction processing (S200) of reconfiguration unit 200 execution.

Fig. 8 is the flow chart that expression convolution filter information converting generates the flow process of processing (S220).

Fig. 9 is the zoning of representation feature amount and the key diagram of the coordinate points on the data for projection.

Figure 10 is the concept map of the relation at the value of expression data for projection and the position of photographing.

Figure 11-the 1st illustrates that convolution filter is of a size of the key diagram of 3 * 3 o'clock convolution algorithm.

Figure 11-the 2nd illustrates that convolution filter is of a size of the key diagram of 1 * 3 o'clock convolution algorithm.

Figure 11-the 3rd illustrates that convolution filter is of a size of the key diagram of 3 * 5 o'clock convolution algorithm.

Figure 12 is the key diagram of the curve shown in the function of the expression standard deviation c of data for projection 211 and smoothing parameter Wa.

Figure 13 is the flow chart of the flow process of expression smoothing techniques (S230).

Figure 14 is the flow chart that expression fft filters information converting generates the flow process of the processing of processing (S240).

Figure 15 is the key diagram of expression Filtering Processing.

Figure 16 is expression by the key diagram of the example of the fft filters function of fft filters input block 340 input, fft filters function that fft filters generation unit 253 generates.

Figure 17 is the regional key diagram with the curve shown in the function of filter function containing ratio of expression standard deviation and high spatial resolution.

Figure 18 is the flow chart of flow process of the processing of expression Filtering Processing (S250).

The specific embodiment

Below, use accompanying drawing to describe the embodiment of X ray CT device of the present invention in detail.In whole accompanying drawings of explanation embodiments of the present invention, give same-sign and omit the explanation of its repetition for the part with identical function.

＜Sketch 〉

At first, based on the Sketch of Fig. 1-1 and Fig. 1-2 application cone-beam X-ray CT of the present invention device.Fig. 1-the 1st, the Sketch figure of cone-beam X-ray CT device of the present invention (C arm mode) 1 is used in expression.Fig. 1-2 is the Sketch figure that the C arm mode cone-beam X-ray CT device 1a that carries in the moving X-ray inspection apparatus of the present invention is used in expression.

Cone-beam X-ray CT device 1 shown in Fig. 1-1 possesses: to subject 2 X-ray irradiations, the X ray of taking subject 2 sees through the photography section 10 of picture 111; Each element of control photography section 10 or see through the control algorithm section 20 of 3 Vc T pictures of picture 111 reconstruct subjects 2 based on X ray.In addition, possess: the display device 80 of displayed map picture; The message input device 70 that is consisted of by mouse, keyboard or trace ball etc. that is used for the position of the image that input shows in display device 80 or parameter.

The C arm mode cone-beam X-ray CT device 1a that carries in the moving X-ray inspection apparatus shown in Fig. 1-2 possesses the 10a of photography section, each element of the control photography 10a of section or the 20a of control algorithm section of reconstruct 3 Vc T pictures.Carried wheel 5 among the cone-beam X-ray CT device 1a, can in inspection chamber, operating room, move.

Fig. 1-1 has described to have rotary middle spindle 4 in the direction parallel with paper, the situation that

x-ray source

11 and 2 dimension X-ray detectors 12 rotate centered by rotary middle spindle 4, relative with it, Fig. 1-2 has described to have rotary middle spindle 4 in the direction vertical with paper,

x-ray source

11 and 2 is tieed up the situation that X-ray detectors 12 slide and rotate in the face parallel with paper, but, the rotation of also can sliding in the face parallel with paper of the cone-beam X-ray CT device 1 of Fig. 1-1, the cone-beam X-ray CT device 1a that carries in the moving X-ray inspection apparatus of Fig. 1-2 also can rotate.

Below, each element shown in the main key diagram 1-1 as required, illustrates the element shown in Fig. 1-2.

(photography section 10)

Photography section 10 possesses: bed 17; To the x-ray source 11 of accumbency at these subject 2 X-ray irradiations on 17; Be oppositely arranged with this x-ray source 11, export the 2 dimension X-ray detectors 12 that X ray sees through picture 111 by detecting the X ray that sees through subject 2; C type arm 13 with

x-ray source

11 and 2 dimension X-ray detectors, 12 mechanical connections; The C type arm holder 14 that keeps this C type arm 13; The ceiling support 15 that this C type arm holder 14 is installed on the ceiling; On 2 dimension directions that can be all around under the illustrated state, support movably the ceiling guide rail 16 of this ceiling support 15; Contrast agent is injected the syringe 18 of subject 2.

X-ray source 11 possesses: produce X ray X-ray tube 11t, will be controlled to be from the direction of the x-ray bombardment of X-ray tube 11t the collimator 11c of circular cone, quadrangular pyramid shape or polygon taper.

The flat panel detector ((flatpanel detector) hereinafter referred to as " FPD ") of example as having used the TFT element in 2 dimension X-ray detectors 12.In addition, as another example of 2 dimension X-ray detectors 12, can use by X ray being seen through x ray image intensifier that picture is transformed to the visible light picture, the picture of x ray image intensifier being carried out the optical lens of imaging and takes the 2 dimension X-ray detectors that the combination of CCD television camera etc. of the visible light picture of the x ray image intensifier by the optical lens imaging consists of.And the photography visuals field of 2 dimension X-ray detectors 12 can be the arbitrary shapes such as circular, square.

Above-mentioned C type arm 13 when the photography of subject 2 centered by rotary middle spindle 4, the camera angle that each rotary moving is predetermined.Thus, above-mentioned

x-ray source

11 and 2 dimension X-ray detectors 12 are kept under the state of relative configuration rotary moving on the circular orbit on the same plane roughly, carry out X-ray.For this rotary moving, there is the photo-geometry parameter of in the image reconstruction computing, using.Have in the photo-geometry parameter: the face that comprises the circular orbit that x-ray source 11 describes owing to C type arm 13 rotary movings is swing-around trajectory face (mid-plane) 3 and rotary middle spindle 4.

(control algorithm section 20)

Control algorithm section 20 possesses: the photography section control unit 110 of control photography section 10; Collection is seen through the image collection unit 110 of picture 111 and storage by the X ray of photography section 10 outputs; See through the reconfiguration unit 200 of picture 111 reconstruct 3 Vc T pictures based on the X ray of collecting; The image-display units 280 that shows the 3 Vc T pictures that reconfiguration unit 200 generates; The convolution filter input block 320 of the formation condition that input reconfiguration unit 200 uses in order to generate convolution filter; The fft filters input block 340 of the formation condition that input reconfiguration unit 200 uses in order to generate Fourier transform (following with Fast Fourier Transform referred to as FFT) wave filter.In addition, described convolution filter is to use convolution algorithm to carry out the images such as smoothing or sharpening coefficient to the pixel value stack of this pixel value and periphery thereof when processing at image space.In addition, so-called fft filters is that per 1 row of 2 dimension image spaces (1 dimension) is carried out the FFT conversion, the coefficient that superposes for each frequency in the capable data that generate by this FFT conversion.In addition, use Fig. 5, Fig. 6 etc. to describe in the back the formation condition that uses in order to generate described convolution filter and the formation condition that uses in order to generate described fft filters in detail.

(photography section control unit 100)

Photography section control unit 100 possesses: the camera chain rotation control unit 101 around the rotary moving of rotary middle spindle 4 of control C type arm 13; The position of control ceiling support 15 on ceiling guide rail 16, the camera chain position control unit 102 that C type arm 13 is carried out 2 dimension controls with respect to the position of subject 2; The x-ray bombardment control unit 103 of the open and close (ON, OFF) of the tube current that flows through among the control X-ray tube 11t etc.; Control syringe 18 injects injection rate and the injection syringe control unit 104 constantly of the contrast agent of subject 2; The bed control unit 105 of the position of subject 2 is adjusted in the position that is used for control bed 17; The X ray of control 2 dimension X-ray detectors 12 sees through the detection system control unit 107 of the photography of picture 111.In addition, the direction of rotation of C type arm 13 as previously mentioned, can there be in the direction parallel with paper rotary middle spindle 4,

x-ray source

11 and 2 dimension X-ray detectors 12 rotate (Fig. 1-1) centered by rotary middle spindle 4, also can there be in the direction vertical with paper rotary middle spindle 4, x-ray source 11 slides in the face parallel with paper with 2 dimension X-ray detectors 12 and rotates (Fig. 1-2), perhaps can possess this two kinds of spinning movements.

(reconfiguration unit 200)

Reconfiguration unit 200 possesses pretreatment unit 210, filter transform information generating unit 220, smoothing unit 230, filter unit 250 and contrary projecting cell 260.

The X ray that pretreatment unit 210 is collected image collection unit 110 sees through the distribution image (hereinafter referred to as " data for projection 211 ") that is transformed to X-ray absorption coefficient as 111.In the present embodiment, at first each pixel data that sees through picture at the X ray that subject 2 and bed 17 is not configured in the air of taking in advance under the states of photography in the visual field is implemented natural logrithm transform operation.Then, each pixel data that sees through picture to subject 2 being placed on the X ray of taking under the state on the bed 17 is implemented the natural logrithm transform operation.Then, see through from the X ray of the air of having implemented above-mentioned natural logrithm transform operation and to deduct subject 2(and the bed 17 of having implemented the natural logrithm transform operation the picture) X ray see through picture, obtain thus data for projection 211.

The element of the filter transform information generating unit 220 that then, comprises among the C arm mode cone-beam X-ray CT device 1a according to cone-beam X-ray CT device (the C arm mode) 1 of Fig. 2 key diagram 1-1 and Fig. 1-2.Fig. 2 is the block diagram of the element of the filter transform information generating unit 220 among expression the present invention.

Filter transform information generating unit 220 is the unit as feature of the present invention, generate smoothing unit 230 and filter unit 250 that use, be used for generating fft filters on convolution filter and the frequency space as the filter transform parameter of image processing filter.Filter transform information generating unit 220 is read in unit 221, ROI setup unit 222, feature amount calculation unit 223, characteristic quantity match unit 224, filter transform information calculations unit 225 and filter transform information storage unit 226 by data for projection and is consisted of.These each elements are by the software of the function by realizing each element and carry out the hardware that computing/control device, input/output unit and the storage device of this software consist of and consist of, by the cooperation of above-mentioned software and hardware, realize the function of each element.

Data for projection reads in unit 221 and reads in the data for projection 211 that is generated by pretreatment unit 210.ROI setup unit 222 is set the zoning of data for projection 211.Near the characteristic quantity (meansigma methods, standard deviation etc.) of the pixel value the each point of feature amount calculation unit 223 calculating data for projection 211 in the zoning that ROI setup unit 222 is set.The characteristic quantity of data for projection 211 each points that characteristic quantity match unit 224 calculates feature amount calculation unit 223 fits to the function of the coordinate figure of data for projection.Filter transform information calculations unit 225 is transformed to the fitting result of characteristic quantity match unit 224 parameter of convolution filter.Filter transform information storage unit 226 is preserved the filter transform parameter as the function of the coordinate figure of data for projection.In addition, the calculating of above-mentioned characteristic quantity need to not calculated by the whole points on the image of data for projection 211, as long as set zoning and calculated characteristics amount about the point in direction appropriate intervals in length and breadth, can obtain the filter transform parameters that data for projection 211 is all put by characteristic quantity match unit 224 and filter transform information calculations unit 225.

The element of the smoothing unit 230 that then, comprises among the C arm mode cone-beam X-ray CT device 1a based on cone-beam X-ray CT device (the C arm mode) 1 of Fig. 3 key diagram 1-1 and Fig. 1-2.Fig. 3 is the block diagram of the element of expression smoothing unit 230.

Smoothing unit 230 uses by the formation condition of the convolution filter of convolution filter input block 320 inputs and filter transform information generating unit 220 and generates and be kept at filter transform parameter in the filter transform information storage unit 226, for each dot generation convolution filter of data for projection 211, and the convolution algorithms that 211 enforcements 2 are tieed up to data for projection.As shown in Figure 3, smoothing unit 230 by the convolution filter information converting read in unit 231, picture element scan unit 232, convolution filter generation unit 233, neighboring pixel read in unit 234, convolution unit 235 and convolution algorithm process after data for projection storage unit 236 consist of.These each elements are by the software of the function that realizes each element and carry out the hardware that computing/control device, input/output unit and the storage device of this software form and consist of, and by the cooperation of above-mentioned software and hardware, realize the function of each element.

The convolution filter information converting reads in unit 231 and reads in the filter transform parameter that is generated by filter transform information generating unit 220.The coordinate figure of picture element scan unit 232 scanning projection data 211 (pixel value of coordinate and this coordinate), convolution filter generation unit 233 generates the convolution filter corresponding with the each point of data for projection according to formation condition and the filter transform parameter of convolution filter.The 232 pairs of data for projection 211 in picture element scan unit scan, and read in the coordinate figure (pixel value of coordinate and this coordinate) of the each point of data for projection.

Neighboring pixel reads in unit 234 based on the coordinate figure by picture element scan unit 232 scanning, reads near the value (pixel value) of data for projection of point (hereinafter referred to as " neighboring pixel ") of the point (hereinafter referred to as " projected pixel ") of the formation object that becomes convolution filter.Convolution unit 235 is about projected pixel, value (pixel value) and neighboring pixel for projected pixel read in the value of the projected pixel of reading in unit 234 and the value of neighboring pixel, use the convolution filter that is generated by convolution filter generation unit 233 and carry out convolution algorithm.Data for projection storage unit 236 was preserved the convolution algorithm result after convolution algorithm was processed.

The element of the filter unit 250 that then, comprises among the C arm mode cone-beam X-ray CT device 1a based on cone-beam X-ray CT device (the C arm mode) 1 of Fig. 4 and Figure 15 key diagram 1-1 and Fig. 1-2.Fig. 4 is the block diagram of the element of expression filter unit 250.Figure 15 is the key diagram of expression Filtering Processing.

Filter unit 250 uses the filter transform parameter that generates by the formation condition of the fft filters of fft filters input block 340 inputs and filter transform information generating unit 220, generate with the data for projection of having implemented convolution algorithm (hereinafter referred to as " convolution algorithm process after data for projection ") 212 respectively walk crosswise corresponding fft filters, the processing of enforcement fft filters.As shown in Figure 4, filter unit 250 by the fft filters information converting read in unit 251, row data read in unit 252, fft filters generation unit 253, FFT unit 254, fft filters integrating unit 255, contrary FFT unit 256 and filter process after data for projection storage unit 257 consist of.The software of the function of these each elements by realizing each element and carry out the hardware that computing/control device, input/output unit and the storage device of this software form and consist of, by above-mentioned software and hardware cooperation, realize the function of each element.

The fft filters information converting reads in unit 251 and reads in by filter transform information generating unit 220 and generate and be kept at filter transform parameter in the filter transform information storage unit 226.The row data are read in unit 252 and are once read in from data for projection 212 and carry out walking crosswise of Filtering Processing and walk crosswise data 352 data, for example Figure 15.Fft filters generation unit 253 generates fft filters according to formation condition and the filter transform parameter of fft filters for every row.FFT unit 254 will be walked crosswise data 352 and be transformed to frequency data, the fft filters that fft filters integrating unit 255 pairs of frequency data integratings fft filters generation unit 253 generates.Contrary FFT unit 256 reverts to the real space data with frequency data, preserves the filter process result by data for projection storage unit after the filter process 257.

Contrary projecting cell 260 carries out the contrary project of data for projection after the filter process, 3 Vc T pictures of generation subject 2.

(convolution filter input block 320)

Convolution filter input block 320 is set the formation condition of the 2 dimension convolution filters that generated by convolution filter generation unit 233.Below, the example of the GUI that convolution filter input block 320 uses is described based on Fig. 5.Fig. 5 is the schematic diagram that the expression convolution filter is set an example of picture 30.

The label 41～44th of Fig. 5, label is selected at the photography position, can set respectively the convolution filter formation condition to various photographies positions such as head, chest, abdominal part, waists, and Fig. 5 has represented to select the chest condition to set the situation of label 42.Button 45 is that button is appended at the photography position, can append the condition at other photography positions such as cervical region, extremity.List box 31 is list boxes of selecting horizontal convolution filter size, can select the value of " 1 ", " 3 " or " 5 ".

List box 32 is to select the longitudinally list box of convolution filter size, can select the value of " 1 ", " 3 " or " 5 ".But, in the situation that selected convolution filter size " 1 " expression not carry out laterally or convolution algorithm (set and close (OFF)) longitudinally in the

list box

31,32.

The

point

33 and 35 of Fig. 5 is convolution filter function threshold set points laterally or longitudinally, can drag to the left and right to make horizontal filter function threshold value μ a or longitudinally filter function threshold value μ b change.In this said " filter function threshold value ", it is the value that regulation is carried out smoothing techniques (in other words, what kind of degree carrying out sharpening with processes) with what kind of degree.When the user wishes relatively low noise image, need to carry out relative to the earth smoothing techniques (in other words, carry out sharpening processes relatively littlely).In this case, be relatively little value with the filter function threshold setting.On the other hand, when the user wishes relatively high-resolution image, need carry out smoothing techniques (in other words, carrying out relative to the earth sharpening processes) relatively littlely.In this case, be relatively large value with the filter function threshold setting.

In addition,

point

34 and 36 is convolution filter function amount set points laterally or longitudinally, by changing the slope of filter function line threshold boundary, can change horizontal filter function variable quantity β a or filter function variable quantity β b longitudinally.At this said " filter function variable quantity ", be to be defined in to carry out relative to the earth the filter function used in the situation of smoothing techniques and relative value of carrying out the variable quantity in the filter function zone of using in the situation of smoothing techniques littlely.Relation about the size of the size of the relation of the size of the size of filter function threshold value and smoothing techniques and filter function variable quantity and smoothing techniques further specifies in " parameter of Fermi distribution function " described later.Illustrate that in the back convolution filter generation unit 223 uses above-mentioned filter function threshold value μ a, μ b and filter function variable quantity β a, β b to generate the details of the processing of convolution filter.

(fft filters input block 340)

Fft filters input block 340 is set the formation condition of the fft filters of fft filters generation unit 253 generations.Below, the example of the GUI that fft filters input block 340 uses is described based on Fig. 6.Fig. 6 is the schematic diagram that the expression fft filters is set an example of picture 40.Identical with Fig. 5, label 41～44th, label is selected at the photography position, and button 45 is that button is appended at the photography position.Fig. 6 has represented to select the chest condition to set the situation of label 42.

List box 51 is to select the high spatial resolution zone list box of filter function, and list box 52 is to select the low contrast regions list box of filter function, the formation condition of selecting fft filters generation unit 253 to use.Point 53 is fft filters function threshold set points, and point 54 is fft filters function amount set points, makes fft filters function threshold μ by dragging to the left and right _F, or the slope variation of line threshold boundary, can change thus fft filters function amount β _FAt this said " fft filters function threshold μ _F", be the value of the size of the regulation smoothing techniques that uses fft filters.In addition, so-called " fft filters function amount β _F" be the value that is defined in the ratio of the variation of two filter functions (filter function 1 among Fig. 6 and filter function 2) of use in the fft filters processing.Illustrate that in the back fft filters generation unit 253 uses above-mentioned filter function threshold value μ _F, filter function variable quantity β _F, and selected high spatial resolution zone generate the details of the processing of fft filters with filter function with filter function, low contrast regions.

Above-mentioned cone-beam X-ray CT device 1 and the specification of 1a are for example lower.The distance of x-ray source 11 and rotary middle spindle 4 is 800mm, rotary middle spindle 4 and 2 dimension X-ray detector 12(FPD) the distance of the X ray plane of incidence be that 400mm, the X ray plane of incidence are the rectangle of 400 * 300mm size, the TFT parts number is 2048 * 1536, and element spacing is 0.2mm.When X ray incides FDP, at first be transformed to light at the X ray plane of incidence by luminous bodys such as CsI, optical signal is transformed to electric charge by photoelectric diode.The electric charge of savings is transformed to digital signal for every certain frame per second by the TFT element and is read out.Under the revolving camera pattern, the TFT element of in bulk 2 * 2 is read X ray with picture size 1024 * 768, pel spacing 0.4mm, per second 30 frames and is seen through picture 111.Camera chain rotation control unit 101 makes 2 dimension X-ray detectors 12 move to the right-hand lay (+100 degree) of subject 2 by ceiling direction (0 degree) from the direction (100 degree) of the left hand of subject 2.Thus, take the X ray of the subject 2 of crossing over 200 projection angles of spending through picture 111.The rotary speed of C type arm 13 for example is per 1 second 40 degree, and be 5 seconds sweep time.

The summary of＜action 〉

The summary of the action in the photography of cone-beam X-ray CT device 1 then, is described.

In cone-beam X-ray CT device 1, at first, camera chain rotation control unit 101 begins the rotation of C type arm 13 centered by rotary middle spindle 4.After during the process Spin-up, x-ray bombardment control unit 103 is from X-ray tube 11t X-ray irradiation, and the shooting of X-ray detectors 12 is tieed up in 107 beginnings 2 of detection system control unit.After seeing through subject 2, be taken into 2 dimension X-ray detectors 12 from the X ray of X-ray tube 11t irradiation.The signal X ray that conduct is made of digital signal after through the A/D conversion of 2 dimension X-ray detectors 12 sees through and is recorded in the image collection unit 110 as 111.The standard scan pattern of 2 dimension X-ray detector FDP is per second 30 frames, and the projection angle in the revolving camera is spaced apart 1.33 degree, obtains 150 pieces of X ray between 5 seconds and sees through picture 111.When the revolving camera of 200 degree was finished, x-ray bombardment control unit 103 finished the x-ray bombardment of X-ray tube 11t, and camera chain rotation control unit 101 is stopping the rotation after during the rotational delay.

In addition, for example use the specification example in the situation of combination of x ray image intensifier, optical lens and CCD television camera as 2 dimension X-ray detectors 12, the diameter of x ray image intensifier is that the standard scan pattern of 300mm, CCD television camera is that per second 60 frames, number of scanning lines are 512, perhaps be 1024 of per second 30 frames, number of scanning lines, the CCD television camera looks like to photograph to the visible light of the x ray image intensifier by the optical lens imaging.The X ray of CCD shot with television camera sees through picture and be carried out the A/D conversion after being transformed to video signal, and the digital picture as 512 * 512 or 1024 * 1024 is collected by image collection unit 110.

Reconfiguration unit 200 is in above revolving camera action or read immediately X ray from image collection unit 110 through picture 111 after the revolving camera release, sees through as 111 based on this X ray and is reconstructed computing, 3 Vc T pictures of generation subject 2.Image-display units 280 is presented at 3 Vc T pictures in the display device 80 that is made of CRT device or LCD device etc.In addition, image-display units 280 also is used to be presented at the X ray of record in the image collection unit 110 through picture 111.The X ray that 200 pairs of reconfiguration units are collected by image collection unit 110 see through as 111 and are reconstructed, and generate thus the reconstructed image of subject, and image-display units 280 shows reconstructed image in display device 80.

＜reconstruction processing 〉

Then, based on the flow process of Fig. 7 explanation by the reconstruction processing (S200) of reconfiguration unit 200 execution.Fig. 7 is that expression is by the flow chart of the flow process of the reconstruction processing (S200) of reconfiguration unit 200 execution.Below, illustrate according to the step order of Fig. 7.

(step S210)

The subject 2 that 210 pairs of image collection unit of pretreatment unit 110 are collected and the X ray of air see through picture 111 and implement the natural logrithm transform operation, are transformed to data for projection 211(S210).

(step S220)

Filter transform information generating unit 220 is calculated near the characteristic quantity (for example meansigma methods Ac or the standard deviation c of near the pixel value of the pixel the each point) of each point of data for projection 211, generates the convolution filter transformation parameter (S220) that is used for generating at step S230 convolution filter.

(step S230)

Convolution filter transformation parameter, the user that smoothing unit 230 uses step S220 to generate uses the formation condition of the convolution filter of convolution filter input block 320 settings in advance, for each dot generation convolution filter of data for projection 211, implement the convolution algorithm (S230) of 2 dimensions for each point.

(step S240)

Filter transform information generating unit 220 is calculated characteristic quantity (the meansigma methods A of the pixel value of respectively walking crosswise data of the data for projection 212 of having implemented the convolution algorithm processing _F, standard deviation _F), generate the fft filters transformation parameter (S240) that is used for generating at step S250 fft filters.

(step S250)

Filter unit 250 uses the fft filters transformation parameter of step S240 generation and the formation condition that the user uses the fft filters of fft filters input block 340 settings in advance, generate with implemented data for projection 212 that convolution algorithm processes respectively walk crosswise corresponding fft filters, enforcement fft filters processing (S250).

(step S260)

Contrary projecting cell 260 uses the data for projection after the fft filters of step S250 is processed to carry out contrary project (S260).

(step S270)

Whether differentiate for whole data for projection and carried out processing from step S210 to step S260.Return step S210 in the situation that whole data for projection are not processed (no), for next processing of data for projection execution from step S210 to step S260.In the situation that "Yes" finishes reconstruction processing (S220), 3 Vc T pictures (S70) of output subject 2.

Below, use Fig. 8, Fig. 9, Figure 10 and Figure 12 explanation as the details of processing separately feature of the present invention, above-mentioned steps S220, S230, S240 and step S250.Fig. 8 is the flow chart that expression convolution filter information converting generates the flow process of processing (S220), Fig. 9 is the zoning of representation feature amount and the key diagram of the coordinate points on the data for projection, Figure 10 is the concept map of the relation at the value (below be also referred to as " projection rank ") of expression data for projection and photography position, and Figure 12 is the key diagram that represents the curve shown in the function of the standard deviation c of data for projection 211 and smoothing parameter Wa.

At first, each the step explanation convolution filter information converting according to Fig. 8 generates processing.

(step S221)

Data for projection reads in unit 221 and reads in the data for projection 211(S221 that generates among the step S210).

(step S222)

As shown in Figure 9, ROI setup unit 222 is set the rectangle of the characteristic quantity that is used for calculating data for projection 211 or the ROI(zoning 239 of tetragonality) size.The ROI size for example is made as 15 * 15～25 * 25 pixels (S222) centered by coordinate points 238.

(step S223)

Coordinate points on the feature amount calculation unit 223 scanning projection data 211 is calculated meansigma methods Ac and the standard deviation c of the pixel value in the ROI zone (zoning 239) of appointment in step S222, obtains thus the characteristic quantity of the each point of data for projection 211.At this moment, because the data that significantly depart from from meansigma methods are affected, once make the block diagram that is made as transverse axis with meansigma methods, maximum, the minima of the pixel value in this ROI for every ROI for the value of calculation that suppresses standard deviation.And, only use the data in for example ± 1/10 number of degrees distribute to obtain standard deviation value (S223) the meansigma methods of pixel value that can be in ROI.In addition, in the present embodiment, obtain characteristic quantity for the each point of data for projection 211, but also can not obtain characteristic quantity for whole points, and only obtained characteristic quantity for the point after the suitable rejecting.In this case, the characteristic quantity of the point of disallowable data for projection 211 can utilize the characteristic quantity of the pixel value that obtains from the zoning that comprises this point.

Figure 10 conceptually represents to cross from chest the variation of value the photography at position of abdominal part, data for projection.In chest region, the X ray absorbtivity is little, and therefore, the meansigma methods of the data for projection after the logarithmic transformation is little, and error (standard deviation) is also little.On the other hand, the data for projection meansigma methods in abdomen area after the logarithmic transformation is large, and the output valve of X-ray detector is little, therefore becomes the large data of error.

The present invention realizes a kind of X ray CT device, the photography position that it can be little in the meansigma methods of data for projection, standard deviation is little is implemented the sharpening wave filter and is generated the X ray CT picture of high spatial resolution, and implement the smoothing wave filter at the large photography position of the error of data for projection and suppress noise, generate the outstanding X ray CT picture of low contrast resolution.

(step S224)

The function (that is, the correspondence of the characteristic quantity of the pixel value of the laterally and longitudinally positional information (coordinate figure) of the each point of data for projection 211 and this position) that the characteristic quantity of data for projection 211 each points that characteristic quantity match unit 224 will calculate in step S223 fits to the coordinate figure of data for projection (S224).In addition, also can omit step S223 and S224.In this case, for example can according to position or the photography conditions predictive value by the characteristic quantity (or scope of characteristic quantity) of user's input pixel value of photographing, use the characteristic quantity of the pixel value of this input to calculate following filter transform information.

(step S225)

Filter transform information calculations unit 225 fitting results with step S224 are transformed to the parameter of convolution filter, namely use the parameter (S225) of the characteristic quantity generation convolution filter of the pixel value that comprises in the fitting result.Below based on Figure 12 the parameter of this convolution filter and the details of processing thereof are described.Figure 12 is the key diagram of the curve shown in the function of the expression standard deviation c of data for projection 211 and parameter Wa.

In general, convolution filter is carried out standardization, so that its total becomes 1.And can import can Varying parameters, for example laterally the parameter Wa of (u direction among Figure 11 described later-1～Figure 11-3) and vertically the parameter Wb of (the v direction among Figure 11 described later-1～Figure 11-3) under 1 the condition of adding up to of convolution filter.Horizontal parameter Wa and longitudinally parameter Wb usually get and surpass-0.5 real number value, be made as maximum with 1.0.

Convolution algorithm when parameter Wa or parameter Wb get negative value becomes the computing that obtains with the difference of adjacent pixels, plays a role as the sharpening wave filter in this case.In description of the present embodiment, suppose that below parameter Wa and parameter Wb get on the occasion of (0.0 ~ 1.0), convolution algorithm plays a role as the smoothing wave filter, carries out sharpening and process to illustrate in the fft filters calculating process of back.Therefore, in the explanation of following smoothing techniques, parameter Wa or parameter Wb are recited as smoothing parameter Wa or smoothing parameter Wb.

Below, the filter transform information calculations unit 225 of enumerating step S225 determines that according to the characteristic quantity (ROI meansigma methods Ac, standard deviation c) of the data for projection 211 that the feature amount calculation unit 223 of described step S223 calculates an example of the functional expression of parameter Wa and Wb illustrates.As mentioned above, suppose that smoothing parameter Wa and Wb get 0.0 ~ 1.0 value.On the other hand, the characteristic quantity of data for projection (ROI meansigma methods Ac, standard deviation c), typically Ac gets the X-ray absorption coefficient of 0.02/mm(water) * 200mm(health thickness)=4.0, σ c gets the value about 0.2, but arbitrarily real number value is got in supposition.As being input as real number value arbitrarily, being output as an example of 0～1 function, " Fermi distribution function " f (x) that gives an example below can importing,

[mathematical expression 1]

f (x) = \frac{1}{1 + e^{x}},

x = \frac{μ_{a} - σ_{c}}{\sqrt{A_{C}}} \cdot β_{a} - - - (1)

Wa=f (x) perhaps similarly imports function f (y),

[mathematical expression 2]

f (y) = \frac{1}{1 + e^{y}},

y = \frac{μ_{b} - σ_{C}}{\sqrt{A_{C}}} \cdot β_{b} - - - (2)

Wb=f(y)。The μ a of formula (1) and formula (2) and μ b are laterally and the longitudinally filter function threshold values by convolution filter input block 320 input, and β a and β b are the filter function variable quantities.According to the item of following explanation, β a and β b study plot can be got the value about 10." Fermi distribution function " of formula (1) and formula (2) have f (x)+f (x)=1 such character, in calculating Figure 11 described later-1～Figure 11-3, can utilize in the computing of the convolution filter of expression for example 1-Wa=f (x) or 1-Wb=f (y).

The curve of Figure 12 (1) (in Figure 12, describing with solid line) expression " Fermi distribution function " f (x), f (0)=0.5 when x=0 is standard deviation c=filter function threshold value μ a.F (x) is about 0.73 when x=-1.0, be 0.5 when x=0, is about 0.27 value when x=+1.0.Smoothing parameter Wa by function f (x) decision, when the ROI of data for projection meansigma methods Ac, filter function threshold value μ a and filter function variable quantity β a do not change, the standard deviation c(of data for projection is noisiness) larger, it is less that x becomes, and smoothing parameter Wa becomes larger.Namely, in general, among " Fermi distribution function " f (x), when filter function threshold value μ=standard deviation smoothing parameter Wa=0.5, when μ＜σ Wa 0.5, as μ〉Wa＜0.5 during σ, at Wa〉0.5 o'clock carry out smoothing techniques relatively largely, less ground carries out smoothing techniques when Wa＜0.5.In addition, at μ〉x increases relatively when making filter function variable quantity β (β＞0) relatively large under the condition of σ, and therefore, smoothing parameter W reduces relatively, has set stronger High-resolution Processing.On the other hand, when making filter function variable quantity β (β＞0) relatively large under the condition of μ＜σ, x reduces relatively, and therefore, smoothing parameter W increases relatively, sets stronger low noise and processes.

The curve of Figure 12 (2) (with dashed lines is described in Figure 12) expression is distinguished filter function threshold value μ a the variation of ± 0.2 o'clock f (x) when meansigma methods Ac and filter function variable quantity β a are standard value Ac=0.4, β a=10.When Ac=4.0, β a=10, during with filter function threshold value μ a+0.2, the x of formula (1) increases 1.0, and for identical standard deviations c, smoothing parameter Wa reduces, and has set High-resolution Processing.

Otherwise when with filter function threshold value μ a-0.2, the x of formula (1) reduces 1.0, and smoothing parameter Wa increases, and has set the low noise processing.Its result compares with the curve (1) of standard setting and to have carried out the low noise setting, is equivalent to curve (3) (with dashed lines is described in Figure 12) in Figure 12.

It more than is the explanation of calculating the situation of horizontal smoothing parameter Wa according to filter function threshold value μ a, filter function variable quantity β a and ROI meansigma methods Ac, standard deviation c, but by a in the above-mentioned record is replaced with b, in Figure 12, a is replaced with b, calculate longitudinally smoothing parameter Wb.

In addition, as previously mentioned, horizontal smoothing parameter Wa being suppressed to be little value, increase longitudinally smoothing parameter Wb, is desirable from the viewpoint of the spatial resolution of CT picture.Represented that in above-mentioned Fig. 5 the horizontal filter function threshold value μ a that puts 33 expressions is set to relatively large value, the longitudinally filter function threshold value μ b of point 35 expressions is set to the situation of relatively little value.

Carry out the processing of this step for the each point of data for projection 211, generate the information that the coordinate figure of each point and smoothing parameter Wa and Wb are mapped.

(step S226)

Filter transform information storage unit 226 is preserved the filter transform information that step S225 obtain (the convolution filter transformation parameter being made as the information of function of the coordinate figure of data for projection) (S226).

Then, use Figure 11-1, Figure 11-2, Figure 11-3 and Figure 13 that the details of smoothing techniques (S230) is described.Figure 11-the 1st illustrates that convolution filter is of a size of the key diagram of 3 * 3 o'clock convolution algorithm, Figure 11-the 2nd illustrates that convolution filter is of a size of the key diagram of 1 * 3 o'clock convolution algorithm, Figure 11-the 3rd illustrates that convolution filter is of a size of the key diagram of 3 * 5 o'clock convolution algorithm, and Figure 13 is the flow chart of the flow process of expression smoothing techniques (S230).

Below, describe according to the step order of Figure 13.

(step S231)

The convolution filter information converting reads in unit 231 and reads in the convolution filter information converting and generate to process convolution filter information converting (the smoothing parameter Wa and the Wb that preserve as the function of the coordinate figure of data for projection by step S226 specifically) that (S220) generate (S231).

(step S232)

The coordinate figure of the each point (hereinafter referred to as projected pixel) of picture element scan unit 232 scanning projection data 211 (suitable with coordinate and the pixel value of pixel) (S232).

(step S233)

Convolution filter generation unit 233 uses the convolution filter information converting to read smoothing parameter Wa, the Wb corresponding with the coordinate figure of each projected pixel, uses them to generate the convolution filter (S233) corresponding with each projected pixel.

At this, use Figure 11-1～Figure 11-3 and Figure 12 for example the processing of the convolution algorithm in the present embodiment and convolution filter generation unit 233 to be described.In addition, convolution algorithm and convolution filter generation method are not limited to following content, can suitably change in the scope that does not break away from technological thought of the present invention.

Figure 11-the 1st, the figure of the convolution algorithm that schematically represents laterally, carries out when the convolution filter size all is " 3 " longitudinally, Figure 11-the 2nd represents that schematically horizontal convolution filter is of a size of " 1 " (namely, horizontal convolution algorithm closes (OFF)), the figure of the convolution algorithm of carrying out when convolution filter is of a size of " 3 " longitudinally, Figure 11-the 3rd represents that schematically horizontal convolution filter is of a size of " 3 ", the figure of the convolution algorithm carried out when convolution filter is of a size of " 5 " longitudinally.Value P (u, v) and near its pixel value of putting of the pixel of convolution algorithm implemented in the matrix 61 of Figure 11-1,63 and 65 expressions.Matrix 62,64 and 66 expression convolution filters.And, for Figure 11-1, calculate the pixel value P (u front with convolution algorithm based on following (3) formula, v) pixel value the P ' (u behind the corresponding convolution algorithm, v), for Figure 11-2, calculate the pixel value P (u front with convolution algorithm based on following (4) formula, v) the pixel value P ' (u, v) behind the corresponding convolution algorithm.

[mathematical expression 3]

P^{'} (u, v) = P (u - 1, v - 1) \times \frac{Wa \cdot Wb}{(1 + 2 Wa) (1 + 2 Wb)} + P (u, v - 1) \times \frac{Wb}{(1 + 2 Wa) (1 + 2 Wb)} + P (u + 1, v - 1) \times \frac{Wa \cdot Wb}{(1 + 2 Wa) (1 + 2 Wb)}

+ P (u - 1, v) \times \frac{Wa}{(1 + 2 Wa) (1 + 2 Wb)} + P (u, v) \times \frac{1}{(1 + 2 Wa) (1 + 2 Wb)} + P (u + 1, v) \times \frac{Wa}{(1 + 2 Wa) (1 + 2 Wb)}

+ P (u - 1, v + 1) \times \frac{Wa \cdot Wb}{(1 + 2 Wa) (1 + 2 Wb)} + P (u, v - 1) \times \frac{Wb}{(1 + 2 Wa) (1 + 2 Wb)} + P (u + 1, v - 1) \times \frac{Wa \cdot Wb}{(1 + 2 Wa) (1 + 2 Wb)} - - - (3)

[mathematical expression 4]

P^{'} (u, v) = P (u, v - 1) \times \frac{Wb}{(1 + 2 Wb)} + P (u, v) \times \frac{1}{(1 + 2 Wb)} + P (u, v + 1) \times \frac{Wb}{(1 + 2 Wb)} - - - (4)

In addition, for Figure 11-3, also same with the formula (4) of the formula (3) of Figure 11-1 and Figure 11-3, multiply by weight in the matrix 66 with position same position in the matrix 65 of this pixel value by the pixel value at matrix 65, pixel value P ' (u, v) behind the calculating convolution algorithm.

The convolution filter of record in the

matrix

62,64 and 66 is the smoothing parameter Wa that generates by filter transform information generating unit 220, the convolution filter that uses smoothing parameter Wa, adds up to 1 mode by standardization with it.

The spatial resolution of reconstruct CT picture largely exists with ... the laterally resolution of the data for projection 211 of (u direction).Therefore, laterally the smoothing parameter Wa of (u direction) is suppressed to 0 or little value, can increase the vertically smoothing parameter Wb of (v direction).In addition, the size of convolution filter to Figure 11-3 for example the expression, can with 3 * 3 as standard, be got 1 * 3 or 3 * 5 size such as Figure 11-1.In the present embodiment, set in the

list box

31,32 of picture 30 at the convolution filter of Fig. 5, when horizontal convolution filter size input 3 and when the convolution filter size inputs 3 longitudinally, for the convolution filter of each dot generation 3 * 3 size of data for projection 211.

(step S234)

Neighboring pixel reads in the pixel value (S234) that unit 234 reads the projected pixel (being also referred to as neighboring pixel) of the periphery of the projected pixel that is positioned at the object that becomes convolution algorithm.The projected pixel that is arranged in periphery is used at following convolution algorithm.

(step S235)

The projected pixel of reading among the convolution filter that convolution unit 235 uses generate in step S233 and step S232, the S234 and the pixel value of neighboring pixel carry out convolution algorithm (S235).Convolution unit 235 for example when setting 3 * 3 filter size in the convolution filter setting picture at Fig. 5, is carried out convolution algorithm according to formula (3).

(step S236)

The convolution algorithm result (S236) that data for projection storage unit 236 was preserved step S236 after convolution algorithm was processed.

(step S237)

Differentiate and whether carried out the processing of step S232 to step S236 for whole projected pixel.When the projected pixel that is untreated whole, return step S232 in the situation of (no), for next processing of projected pixel execution from step S232 to step S236.In the situation that "Yes" finishes smoothing techniques (S230), advance to the fft filters information converting and generate processing (S240).

Then, illustrate that based on Figure 14 and Figure 15 the fft filters information converting generates the details of processing (S240).Figure 14 is the flow chart that expression fft filters information converting generates the details of the processing of processing (S240), and Figure 15 is the key diagram of expression Filtering Processing.In addition, the ordinate 24 of Figure 15 is lines of projection to 2 dimension X-ray detectors 12 of expression rotary middle spindle 4, for carrying out Filtering Processing along the data 352 of walking crosswise of direction of rotation (direction vertical with rotary middle spindle 4).Below, describe according to the step order of Figure 14.

(step S241)

Data for projection reads in unit 221 and reads in the rear data for projection 212(S241 of convolution algorithm processing that generates among the step S230).

(step S242)

The ROI setup unit 222 settings rectangle ROI(zoning 342 of growing crosswise shown in Figure 15) size (S242).

(step S243)

Feature amount calculation unit 223 is after convolution algorithm is processed on the data for projection 212, in above-below direction (perhaps being also referred to as vertically) scanning rectangle ROI(zoning 342), calculated characteristics amount (the meansigma methods A of the pixel value of the interior pixel of ROI for example _F, standard deviation _F).At this moment, identical during with the calculating of step S223, in order to suppress to be affected owing to the data that significantly depart from from meansigma methods make the value of calculation of standard deviation, can once generate meansigma methods with the pixel value in the ROI, maximum, minima as the block diagram of transverse axis, only example is obtained standard deviation value (S243) such as the data in ± 1/10 the number of degrees distribution the meansigma methods of the pixel value in ROI.

(step S244)

The function (that is, the correspondence of the characteristic quantity of the positional information of the above-below direction of data for projection and its position) that the characteristic quantity that characteristic quantity match unit 224 calculates step S243 fits to the coordinate figure relevant with the above-below direction of data for projection (S244).

(step S245)

Filter transform information calculations unit 245 fitting results with step S244 are transformed to the parameter of fft filters.The parameter of this fft filters and the details (S245) of processing thereof below are described.

At this, use Figure 16 and Figure 17 illustrate fft filters function and the synthetic method thereof in the present embodiment.Figure 16 is the key diagram that the example of the fft filters function of fft filters input block 340 inputs and the fft filters function that fft filters generation unit 253 generates is passed through in expression.Figure 17 is the regional key diagram with the curve shown in the function of filter function containing ratio of expression standard deviation and high spatial resolution.In addition, fft filters function and synthetic method thereof are not limited to following situation, can suitably change in the scope that does not break away from technological thought of the present invention.

Figure 16 represents the example by the fft filters function of the fft filters function of fft filters input block 340 inputs and 253 generations of fft filters generation unit.The curve of the top of Figure 16 (a) and the curve (b) of below be the fft filters function of the high spatial resolution zone usefulness by 340 inputs of fft filters input block and the example of the fft filters function that low contrast regions is used.3 curves (with dashed lines is described) of center are according to the characteristic quantity of the data for projection example from the fft filters function of the linearity of two input fft filters functions and generation by fft filters generation unit 253.The longitudinal axis is the integrating intensity on the frequency space of carrying out in the fft filters integrating unit 255, and transverse axis represents frequency, and unit is " 1/Pixel ".

The input picture of present embodiment is 1024 * 768 images that the in bulk (binning) by 2 * 2 is collected, it is the known fact in the FFT computing, but in order not produce obscuring that what is called turns back and cause, suppose with 2 times of the transverse width 1024 of input picture 2048 and carry out the fft filters computing.At this moment, the absolute value of capping frequency (being called as " being Qwest's frequency ") is 1024 from the specimen interval, frequency is-1024 ~+1024 value.The fft filters function is set to the positive negative frequency that equates with absolute value and gets identical value, has represented the only fft filters function of positive frequency in Figure 16.In addition, represented in the example of Figure 16 to use the Shepp-Logan function as high spatial resolution zone with the fft filters function, the fft filters function of using as low contrast regions uses the situation of the sin function in its 1/2 cycle.The fft filters function that generates is as the linearity of two functions and represent, in the high spatial resolution zone that meansigma methods at data for projection is little, standard deviation is little, generate until the larger fft filters of altofrequency value, in the large low contrast regions of error large at X-ray absorption coefficient, data for projection, generate the fft filters that high-frequency value is little, the smoothing degree is large.In addition, all make the slope (differential coefficient) of initial point become equal value in the fft filters function, so that the meansigma methods of reconstruct CT picture equates.

Then, use Figure 17 to enumerate decision high spatial resolution zone with an example of the functional expression of the containing ratio of fft filters function, characteristic quantity (the ROI meansigma methods A that processes rear data for projection 212 in described step S243 according to the convolution algorithm that calculates is described _F, standard deviation _F), the linearity of the fft filters function that fft filters generation unit 253 usefulness high spatial resolutions zones is used with fft filters function and low contrast regions and generate the processing of fft filters.The containing ratio of two input fft filters functions in the fft filters that generates (high spatial resolution zone with, low contrast regions with) adds up to 1.On the other hand, the characteristic quantity of data for projection (ROI meansigma methods A _F, standard deviation _F) as previously mentioned, A typically _FX-ray absorption coefficient for 0.02/mm(water) * 200mm(health thickness)=4.0, σ _FGet the value about 0.2, but arbitrarily real number value is got in supposition.As being input as real number value arbitrarily, being output as the example of 0 ~ 1 function, identical with formula (1), can use " Fermi distribution function " f (x),

[mathematical expression 5]

f (x) = \frac{1}{1 + e^{x}},

x = \frac{σ_{F} - μ_{F}}{\sqrt{A_{F}}} \cdot β_{F} - - - (5)

(definition of variable x is different from formula (1)) are set as the containing ratio that the fft filters function is used in the high spatial resolution zone with f (x).μ _FThe fft filters function threshold by 340 inputs of fft filters input block, β _FIt is the filter function variable quantity.As previously mentioned, with β _FStudy plot is set as the value about 10." Fermi distribution function " has f (x)+f, and (character x)=1 can (x) be made as the containing ratio that low contrast regions is used the fft filters function with f.

Below, in the discussion same with Figure 12 (wherein, the definition of variable x is different from formula (1)), the solid line of Figure 17 is " Fermi distribution function " f (x), the high spatial resolution zone is with the containing ratio f (x) of fft filters function, as the ROI of data for projection meansigma methods A _F, filter function threshold value μ _FAnd filter function variable quantity β _FWhen not changing, the standard deviation F(of data for projection is noisiness) larger, x more increases, and f (x) more reduces.The dotted line of Figure 17 represents as meansigma methods A _FAnd filter function variable quantity β _FValue A for standard _F=4.0, β _F=10 o'clock, with filter function threshold value μ _FThe respectively variation of ± 0.2 o'clock f (x).Work as A _F=4.0, β _F=10 o'clock, when with filter function threshold value μ+0.2, the x of formula (5) reduced 1.0, for the identical standard deviations _F, the high spatial resolution zone increases with the containing ratio f (x) of fft filters function, has set High-resolution Processing.Otherwise, when with filter function threshold value μ _F-0.2 o'clock, the x of formula (5) increased 1.0, and the high spatial resolution zone reduces with the containing ratio f (x) of fft filters function, has set the low noise processing.F (x) is about 0.73 when x=-1.0, be 0.5 when x=0, is about 0.27 value when x=+1.0, is 3 curves of expression for example among Figure 16 with the fft filters function of this numerical generation.Carry out this processing for each row data, generate positional information (coordinate figure) and the regional fft filters information converting that consists of with data corresponding to the containing ratio f (x) of fft filters function of high spatial resolution by the above-below direction (longitudinal direction) of row data.The fft filters information converting can be defined as the containing ratio of fft filters function the function of the coordinate figure relevant with the above-below direction of data for projection.

(step S246)

Filter transform information storage unit 226 is kept at the fft filters information converting (S246) of obtaining among the step S245.

Then, use Figure 15 and Figure 18 that the details of Filtering Processing (S250) is described.Figure 15 is the key diagram of expression Filtering Processing, and Figure 18 is the flow chart of flow process of the processing of expression Filtering Processing (S250).Below, illustrate according to the step order of Figure 18.

(step S251)

The fft filters information converting reads in unit 251 and reads in by the fft filters information converting and generate to process fft filters information converting (the high spatial resolution zone fft filters function containing ratio of preserving as the function of the coordinate figure relevant with the above-below direction of data for projection by step S246 specifically) that (S240) generate (S251).

(step S252)

The row data are read in unit 252 once read the data of walking crosswise of carrying out Filtering Processing the data for projection 212 after convolution algorithm are processed, and for example walk crosswise data 252(S252 among Figure 15).

(step S253)

Fft filters generation unit 253 is for each row data, and the fft filters information converting that reads among the coordinate figure of the above-below direction of use the row data and the step S251 generates the fft filters (S253) corresponding with the up and down coordinate of row data.Fft filters generation unit 253 is based on the fft filters information converting calculating high spatial resolution zone fft filters function containing ratio corresponding with the coordinate figure of the above-below direction of row data.And, generation comprises the regional fft filters with the fft filters function of high spatial resolution that is set by the user input by the GUI picture of Fig. 6 according to the containing ratio that calculates, equally, generate the fft filters (S253) that comprises the fft filters function that low contrast regions that GUI picture by Fig. 6 is set by the user input uses according to (the above-mentioned containing ratio of 1-).

(step S254)

FFT unit 254 will be walked crosswise data 352 and be transformed to frequency data (S254).

(step S255)

The fft filters (S255) that 255 pairs of frequency data integratings of fft filters multiplication unit step S253 generates.

(step S256)

Contrary FFT unit 256 is transformed to frequency data data for projection (S256) after the filter process of real space.

(step S257)

Data for projection (S257) after the filter process that data for projection storage unit 257 preservation step S256 generate after the filter process.

(step S258)

Whether differentiate for all walking crosswise data and carried out processing from step S252 to step S257.Return step S252 in the situation of (no) when whole capable data not being processed, for the processing of next line data execution from step S252 to step S257.In the situation that "Yes" finishes Filtering Processing (S250), advance to contrary projection process (S260).

Above, embodiments of the present invention have been described, but structure described above is an example only, for example generate processing (S220) by omitting smoothing unit 230 and convolution filter information converting, the fft filters information converting that only carries out present embodiment generates the fft filters processing of processing and using this processing, perhaps only carry out smoothing unit 230 and convolution filter information converting generation processing (S220) and come simplified operation processing etc., in the scope that does not break away from technological thought of the present invention, can suitably change.In the situation that the former, replacing with data for projection 211 by data for projection 212 after the convolution algorithm in the above-mentioned embodiment is processed can realize.In addition, as the characteristic quantity of pixel value, used meansigma methods or the standard deviation of the pixel value in the zoning, but characteristic quantity is not limited to meansigma methods or standard deviation, for example can replace meansigma methods and use mode, median, replace standard deviation and use variance.And, by in the value of the meansigma methods of formula (5), standard deviation, using the value that replaces them in formula (1), can play the action effect identical with above-mentioned embodiment.

According to the present invention, for each dot generation convolution filter of data for projection, thus, generate the vertical and horizontal continually varying convolution filter along data for projection.Generate fft filters by the data of respectively walking crosswise corresponding to data for projection after data for projection or the convolution algorithm processing, generate along vertical continually varying fft filters of data for projection or the rear data for projection of convolution algorithm processing.And, a kind of X ray CT device can be provided, it carries out convolution algorithm processing and Filtering Processing by using these continually varying wave filter, can be little in the meansigma methods of data for projection, the photography position that standard deviation is little is implemented the sharpening wave filter and is generated the X ray CT picture of high spatial resolution, and implement the smoothing wave filter at the photography position that the error of data for projection is large, suppress noise, generate the outstanding X ray CT picture of low contrast resolution, can expect to improve head, the radiography photography of abdominal part etc., and tooth jaw, lumbar vertebra, the diagnosis performance of plastic surgery's photography of extremity.

In addition, value and coordinate figure about data for projection, used convolution filter and fft filters that its continuous parameters changes, therefore can be created on high spatial resolution CT as reconstruction region and low contrast CT as the X ray CT picture that does not produce factitious boundary line between the reconstruction region.

Symbol description

1: cone-beam X-ray CT device; 1a: the C arm mode cone-beam X-ray CT device that carries in the moving X-ray inspection apparatus; 2: subject; 3: swing-around trajectory face (mid-plane); 4: rotary middle spindle; 5: wheel; 10: photography section; 10a: the photography section of the C arm mode cone-beam X-ray CT device 1a that carries in the moving X-ray inspection apparatus; The 11:X radiographic source; The 11t:X ray tube; 11c: collimator; 12:2 ties up X-ray detector; 13:C type arm; 14:C type arm holder; 15: the ceiling support; 16: the ceiling guide rail; 17: bed; 18: syringe; 20 control algorithm sections; 20a: the control algorithm section of the C arm mode cone-beam X-ray CT1a that carries in the moving X-ray inspection apparatus; 24: the projection to 2 dimension X-ray detectors 12 of rotary middle spindle 4; 30: convolution filter is set picture; 31: horizontal convolution filter size Selection list box; 32: vertical convolution filter size Selection list box; 33: horizontal convolution filter function threshold set point; 34: horizontal convolution filter function amount set point; 35: vertical convolution filter function threshold set point; 36: vertical convolution filter function amount set point; 40:FFT filter configuration picture; 41: the head condition is set label; 42: the chest condition is set label; 43: the abdominal part condition is set label; 44: the waist condition is set label; 45: button is appended at the photography position; 51: high spatial resolution zone filter function selective listing frame; 52: low contrast regions filter function selective listing frame; 53:FFT filter function threshold set point; 54:FFT filter function variable quantity set point; 61: implement convolution filter and be of a size of 3 * 3 o'clock the pixel of convolution algorithm and near the pixel value of point thereof; The convolution filter of 62:3 * 3; 63 implement convolution filters is of a size of 1 * 3 o'clock the pixel of convolution algorithm and near the pixel value of point thereof; The convolution filter of 64:1 * 3; 65: implement convolution filter and be of a size of 3 * 5 o'clock the pixel of convolution algorithm and near the pixel value of point thereof; The convolution filter of 66:3 * 5; 70: message input device; 80: display device; 100: photography section control unit; 100a: the photography section control unit of the C arm mode cone-beam x-ray ct device 1a that carries in the moving X-ray inspection apparatus; 101: the camera chain rotation control unit; 102: the camera chain position control unit; 103:X roentgenization control unit; 104: the syringe control unit; 105: the bed control unit; 107: the detection system control unit; 110: the image collection unit; The 111:X ray sees through picture; 200: reconfiguration unit; 210: pretreatment unit; 211: data for projection; 212: data for projection after convolution algorithm is processed; 220: the filter transform information generating unit; 221: data for projection reads in the unit; The 222:ROI setup unit; 223: feature amount calculation unit; 224: characteristic quantity match unit; 225: filter transform information calculations unit; 226: filter transform information storage unit; 230: the smoothing unit; 231: the convolution filter information converting reads in the unit; 232: the picture element scan unit; 233: the convolution filter generation unit; 234: neighboring pixel reads in the unit; 235: convolution unit; 236: data for projection storage unit after convolution algorithm is processed; 238: the coordinate points on the data for projection; 239: characteristic quantity calculates ROI; 250: filter unit; 251:FFT filter transform information is read in the unit; 252: the row data are read in the unit; 253:FFT wave filter generation unit; The 254:FFT unit; 255:FFT wave filter integrating unit; 256: contrary FFT unit; 257: data for projection storage unit after the filter process; 260: contrary projecting cell; 280: image-display units; 320: the convolution filter input block; 340:FFT wave filter input block; 342: characteristic quantity calculates ROI; 352: walk crosswise data.

Claims

1. X ray CT device is characterized in that possessing:

Produce the x-ray source of X ray;

Configure relative with described x-ray source detected the described X ray that sees through subject, exports the X-ray detector of the data for projection of described subject;

Make described x-ray source keep the rotary unit that rotates under the state of relative configuration with described X-ray detector;

Generate the wave filter generation unit of the image processing filter that changes accordingly with the characteristic quantity that is included in the pixel value in the described data for projection;

Reconfiguration unit to described data for projection, uses the image processing filter of described generation to be reconstructed computing, generates the X ray CT picture of described subject; And

The image-display units that shows described X ray CT picture.

2. X ray CT device according to claim 1 is characterized in that,

Described wave filter generation unit generates the convolution filter conduct described image processing filter corresponding with the characteristic quantity of the pixel value of this point for the each point of described data for projection,

Described reconfiguration unit possesses the convolution unit for the described convolution filter of each some stack of described each point.

3. X ray CT device according to claim 2 is characterized in that,

Described X ray CT device also possesses:

Input the first input block of the formation condition of described convolution filter; And

Generation comprises and the characteristic quantity of the pixel value of described data for projection the first filter transform information generating unit of the first filter transform information of Varying parameters accordingly,

Described wave filter generation unit uses formation condition and the described first filter transform information of described input, generates described convolution filter.

4. X ray CT device according to claim 3 is characterized in that,

As described formation condition, described the first input block is accepted the horizontal convolution size of described convolution filter, stipulate the filter function threshold value of the size of horizontal smoothing techniques, and the filter function variable quantity of stipulating the variable quantity of horizontal smoothing filter function, and the longitudinally convolution size of described convolution filter, stipulate the longitudinally filter function threshold value of the size of smoothing techniques, and stipulate the longitudinally input of the filter function variable quantity of the variable quantity of smoothing filter function

Described the first filter transform information generating unit is calculated horizontal smoothing parameter with the characteristic quantity of the pixel value of described data for projection and described transversal filter function threshold and transversal filter function amount, and characteristic quantity, described longitudinal filter function threshold and longitudinal filter function amount with the pixel value of described data for projection are calculated vertical smoothing parameter

Described wave filter generation unit is to the each point of described data for projection, use the characteristic quantity of pixel value of this point and horizontal smoothing parameter and the described vertical smoothing parameter corresponding with this characteristic quantity, generate by the horizontal convolution size of described input and the vertical described convolution filter that consists of of convolution size.

5. X ray CT device according to claim 4 is characterized in that,

Described the first filter transform information generating unit also possesses: the first area setup unit of setting the first zoning of the each point that comprises described data for projection; The First Characteristic amount computing unit of the characteristic quantity of the pixel value of the pixel that calculating comprises in described the first zoning; The First Characteristic amount match unit that the characteristic quantity of the coordinate figure of described each point and described pixel value is mapped, described the first filter transform information that generation will use described horizontal smoothing parameter that the characteristic quantity of the pixel value corresponding with described coordinate figure calculates and described vertical smoothing parameter and described coordinate figure to be mapped

Described wave filter generation unit uses coordinate figure and the described first filter transform information of the each point of described data for projection, generates described convolution filter.

6. X ray CT device according to claim 2 is characterized in that,

Described wave filter generation unit, process each row data of the object that becomes 1 dimension Fourier transformation processing of rear data for projection for the convolution algorithm of described data for projection or the described convolution filter that superposeed, characteristic quantity based on the pixel value of the row data generates the fft filters corresponding with frequency, as described image processing filter

Described reconfiguration unit possesses the filter unit that uses the Filtering Processing of described fft filters for each data of each row data of data for projection after each row data of described data for projection or the processing of described convolution algorithm.

7. X ray CT device according to claim 6 is characterized in that,

Described X ray CT device also possesses:

Input the second input block of the formation condition of described fft filters; And

Generation comprises and the characteristic quantity of the pixel value of the capable data of described data for projection the second filter transform information generating unit of the second filter transform information of Varying parameters accordingly,

Described wave filter generation unit uses formation condition and the described second filter transform information of described input, and each the row data for each row data or the described convolution algorithm of described data for projection are processed rear data for projection generate described fft filters.

8. X ray CT device according to claim 7 is characterized in that,

Described the second filter transform information generating unit also possesses:

The second area setup unit of the second zoning that the capable data of data for projection consisted of after setting was processed by described data for projection or described convolution algorithm;

Calculating is included in the Second Characteristic amount computing unit of characteristic quantity of the pixel value of the pixel in described the second zoning; And

The Second Characteristic amount match unit that the coordinate figure of direction that will be vertical with the length direction of described row data and the characteristic quantity of described pixel value are mapped,

The second filter transform information that generation will be used parameter that the characteristic quantity of the pixel value corresponding with described coordinate figure calculates, be mapped with described coordinate figure,

Described wave filter generation unit uses coordinate figure and the described second filter transform information of described each row data, generates described fft filters.

9. X ray CT device according to claim 8 is characterized in that,

As described formation condition, the input of the filter function variable quantity of the filter function threshold value of the size of the containing ratio of the second filter function, described the first filter function of regulation or the second filter function that described the second input block is received in the first filter function of using in the zone of relative high spatial resolution, use in relative low contrast regions, the variable quantity of the described containing ratio of expression

Described the second filter transform information generating unit is calculated the described parameter that is made of the described containing ratio corresponding with the characteristic quantity of the pixel value of described the second zoning,

Described wave filter generation unit is based on described the second filter transform information, calculate described first filter function of described each row data or the containing ratio of described the second filter function, according to this containing ratio described the first filter function and described the second filter function are carried out integrating, generate thus described fft filters.

10. the control method of an X ray CT device, described X ray CT device possesses: the x-ray source that produces X ray; Configure relative with described x-ray source detected the X-ray detector that the described X ray that sees through subject is exported the data for projection of described subject; And make described x-ray source keep the rotary unit that rotates under the state of relative configuration with described X-ray detector,

The control method of described X ray CT device is characterised in that,

Possess following steps:

Generation is according to the step of the image processing filter of the Feature change of the pixel value that comprises in described data for projection;

For described data for projection, use the image processing filter of described generation to be reconstructed computing, generate the step of the X ray CT picture of described subject; And

The step that shows described X ray CT picture.